1. Field of the Invention
The invention relates to a method of operating a webfed rotary printing machine, for example, a newspaper printing machine or a publication printing machine.
2. Description of the Related Art
In such a printing machine, a web is printed by at least one printing unit and a number of web streams are guided above one another by means of turner bars and laid on one another and advance to a folding former, the web in its travel course passing through pull units the lead of which can be set.
It is barely possible for the operator to set the web tension in the folder superstructure of a printing machine, for the reasons cited below. Very often, adjustment facilities for the lead of pull units are not present. If the adjustment facility is present, the operator is displayed only the lead, which he cannot put into order, this display often being inaccurate, for example in the case of precision adjusting mechanisms.
If the operator then makes his settings in accordance with his visual impression in such a way that there are no creases in the folder superstructure, there is no incorrect run and the pins do not tear out, the leads can be set so unfavorably that, in the case of individual electrical drives, e.g., of the pull units, some drives exceed their rated torque but others are considerably underloaded.
If a number of web streams are taken over the folding former, the streams located on the inside can barely be influenced by other pull rolls. A generally recognized setting of the web tensionxe2x80x94at the maximum at the former and less and less towards the outsidexe2x80x94is thus impossible.
When the printing machine is being started up, the web tension dips considerable in the folder superstructure as a result of the influence of throwing the print on, damping solution, ink, silicone, in order then to recover again only slowly. If the dip is too sharp, the web runs off and paper breaks occur.
EP 0 908 310 A2 shows a device for feeding web streams to a folding former, each web stream being allocated a driven roll, over which the web streams are deflected individually and led to the former. The intention is in this way to avoid speed differences between the individual web streams, which are established when the streams, lying on one another, wrap around a pull roll.
It is an object of the invention to provide a method for achieving optimal web tension relationships in the folder superstructure.
According to the invention, the object of maintaining desired web tension values in the folder super structure is achieved by starting up the printing machine at a selected web speed and with print thrown off from the printing unit. Web pull units are disposed in the web course downstream of the printing unit and at locations in a folder superstructure and at a folding former. These pull units each have first and second drive lead values storable in a computing and memory unit. The pull units are operated at first drive lead values to provide optimal tensions in the web. The print is then thrown on in the printing unit and the pull units are operated at the second drive lead values to provide optimal tensions in the web.
Using the method, when the printing machine is started up, even in the case of different paper grades and productions, optimal gradations of the web tension are rapidly obtained on the former and in the entire folder superstructure. As a result, even web tension problems during a production change are eliminated. The method can be automated. Overall, rejects and machine down times (web breaks) can be reduced.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.